The invention relates to the field of testing data communications networks, particularly data communications networks employing optical fibers.
Conventional data communications services, whether implemented in copper transmission wiring or in fiber optic cables, often incorporate testing equipment to determine the current state of a network. The advent of time domain reflectometers has allowed test signals to be sent out over conductors, and if a discontinuity or fault exists at a point along the circuit, a portion of the test signal is reflected back to the source. The time it takes for the reflected signal to return to the source is an indication of the distance along the conductor at which the discontinuity or fault lies. Time Domain Reflectometry (TDR) technology is extremely useful in long runs of cable because it allows the identification of a problem at a particular point along the conduit. With the increasing use of fiber optic technology in data transmission, Optical Time Domain Reflectometers (OTDR) utilize the analogous concepts in testing optical signal transmission.
Prior transmission testing systems and techniques incorporate test signals into live data networks, but each technique has its limitations. For example, the test signal may be sent along non-service frequencies of a usable spectrum. As another example, in the context of optical fibers, portions of a network may incorporate a shutter to allow for testing during particular time intervals. Other systems bring down a certain portion of a network to test a portion of the conductors, such as testing dark fiber for integrity before use. Some of these prior systems utilize time domain reflectometers that are external to the data circuit within the network.